1. Field of the Invention
The invention in general relates to cables having one or more central energy conducting members and particularly to a cable having one or more light energy conducting optical fibers, suitably protected for ruggedized use.
2. Description of the Prior Art
In U.S. Pat. No. 4,553,815 there is described an optical fiber cable construction wherein an optical fiber, preferably surrounded by a low modulus buffer material such as silicone resin, is encased in a liquid crystal polymer protective cladding. The liquid crystal polymer is of the type which is thermoplastic and forms rigid, rod-like molecular aggregates in an overlapping, orientable fashion, at some point in its melt cycle. The buffered optical fiber is placed in a die member of an extruding machine having a conical chamber into which is introduced the liquid crystal polymer material. As the optical fiber is pulled through the die, the liquid crystal polymer is deposited as an annulus which is drawn down over and onto the fiber with the construction and operation being such as to promote orientation of the rod-like molecular aggregates which function as the polymer's self-contained reinforcing elements.
The resulting cable construction provides for a rugged optical fiber cable having high abrasion, impact and rupture resistance with a very high tensile strength normally provided by a fiber impregnated resin coating, however, at a fraction of the thickness so that relatively small diameter spools or drums may be used for storage and deployment of the optical fiber cable.
Maximum orientation of the liquid crystal polymer is typically achieved with wall thicknesses no greater than approximately 0.02 to 0.03 inches. Under some various adverse environmental conditions, a thicker more protective coating would be desirable such as for use as above ground transmission lines where the cable might be strung on poles. If the extruding machine process is modified to deposit the desired thicker coating on the optical fiber, the resulting cable would be subject to a loss of material strength since the polymer would not have the same orientation achievable with the thinner coating. It is believed that this is due to a greater opportunity for turbulent melt mixing of the polymer and reduced shear process.
The present invention provides for a cable construction having an outer liquid crystal polymer jacketing material of a much greater thickness than the 0.02 to 0.03 inch maximum achievable with the construction described in the aforementioned patent, while still maintaining the desired orientation of the molecular aggregates so as to define a high strength cable arrangement.